Gypsy moth damage down, still pesky


WOOSTER, Ohio – This year has been a lousy year for the gypsy moth in Ohio, and we have the rainy spring (and a fungus) to thank for it.

Thousands of forested acres were saved from defoliation this year by Entomophaga maimaiga, a fungal disease that can wipe out large populations of the moth provided wet weather occurs during the spring.

The fungus – first released in Ohio in 1993 – infects the gypsy moth’s caterpillar stage, which is responsible for massive tree defoliation between April and June.

“It’s been so quiet this year I haven’t received a single phone call,” said Dan Herms, entomologist, “which is not surprising because we had the right conditions for the spread of the fungus.”

Damage estimate. Herms is part of the Ohio Agricultural Research and Development Center, which is the research arm of Ohio State University’s College of Food, Agricultural, and Environmental Sciences.

Defoliation data for 2002 is yet to be released, but Herms estimates the damage in Ohio at 5,000 acres or less – peanuts compared to 42,459 acres harmed last year and almost 50,000 in 1999 and 1996.

The gypsy moth fungus has also helped keep defoliation figures down in other states affected by the pest, according to Amy Onken, entomologist.

In 2001, nearly two million acres of woods were devastated by the leaf eaters nationwide.

Destructive. Gypsy moth (Lymantria dispar) is the most destructive pest of forest and shade trees in the eastern United States. Native to Europe and Asia, it was brought into the country in 1869 for breeding experiments with silkworms.

The caterpillars can feed on leaves of more than 300 species of trees and shrubs. Favorites include oaks, aspens, birches, crabapples and willows.

A healthy tree can usually withstand only two years of heavy defoliation before it is permanently damaged or dies. Research has shown that this can lead to oak tree mortality rates as high as 89 percent.

Thus far, the gypsy moth has extended from Canada to North Carolina along the Atlantic coast, and west to Pennsylvania, West Virginia, Ohio, Michigan and Wisconsin. It is expected to continue traveling south and west until infesting most of the United States.

Close to home. In Ohio, the moth has been active in the northeastern counties and along the Lake Erie shore. However, it is quickly moving toward the central and southeastern areas of the state.

“The moth will spread everywhere where forests, especially oak, are present,” Herms said. “When the pest explodes in southeastern Ohio it will be a mess. And that will happen as soon as we have a dry spring.”

Since Entomophaga maimaiga is only as reliable as the weather, the Ohio Department of Agriculture has been offering free suppression treatments to property owners in an attempt to slow down the moth’s frantic pace and prevent major defoliation in the state.

“It’s very important that property owners apply for a test to know the level of infestation they have,” said Kelly Harvey, manager of the Gypsy Moth Suppression Program, which began work in 1990.

“The minimum to qualify is 250 egg masses per acre in a residential area and 1,000 egg masses per acre in a forest.”

Suppression. More than 16,000 acres in 21 counties were treated as part of the suppression program last May. Ohio Department of Agriculture employs low-flying crop dusting planes to spray non-harmful insecticides such as BT, Dimilin and GypCheck.

But spraying isn’t enough to minimize the effect of the gypsy moth.

According to Harvey, the biggest challenge is education.

“The best way to tackle this problem is to learn about the real impact of gypsy moth, monitor its development and take preventive measures,” Harvey said. “But most people don’t seek help until their beloved 100-year-old oaks are so damaged they have to be cut down.”

For more information call 614-728-6400 or visit


Up-to-date agriculture news in your inbox!